Environmental Geochemistry, GLY 4241/5243, © David Warburton, 2015
LECTURE 15 Petroleum and the Environment - Part 2
Note: Slide numbers refer to the PowerPoint presentation which accompanies the lecture.
Petroleum 1, slide 1 here
INTRODUCTION
Petroleum 1, slide 2 here
The use of petroleum and its derivatives represents a massive threat to the environment.
Petroleum is used in huge quantities, and the use of petroleum has been increasing very rapidly,
as Table 15-1 shows.
Table 15 - 1 Petroleum Consumption, 1960 - 2005
Year
Consumption, millions of barrels per day
United States
China
World
1960
9.80
0.17
21.34
1965
11.51
0.25
31.14
1970
14.70
0.62
46.81
1975
16.32
1.36
56.20
1980
17.06
1.77
63.11
1985
15.73
1.89
60.09
1990
16.99
2.30
66.55
1995
17.72
3.36
69.91
2000
19.70
4.80
76.69
2005
20.80
6.72
83.65
2010
19.14a
8.23a
87.82a
2015
19.40a
11.97
95.01a
Sources: 1960-1979—Energy Information Administration (EIA), International Energy Database. 1980 forward—EIA, "International Energy Annual 2009"
(March 2009). From table 11.10 on the Energy Information Administration, 2009
BP Statistical Review of World Energy, 2016
a
World petroleum consumption quadrupled from 1960 to 2008.
Petroleum 1, slide 3 here
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Environmental Geochemistry, GLY 4241/5243, © David Warburton, 2015
Starting in 2008, the world entered a deep recession, and oil consumption slowed in 2009.
The United States is the leading petroleum consuming country. Chinese consumption has
increased much faster than the rest of the world. Oil consumption in China is expected to
increase 4 percent a year, and by 2025 China is projected to be the second largest oil consuming
country in the world, accounting for 11 percent of total world consumption. During the period
1980 - 1995, United States consumption hardly increased. Since 2005, U.S. annual consumption
has dropped. (Hirsch et al., 2005) As the projection on the graph from 2006 shows, the
developing world, lead by China, has been increasing consumption very rapidly. Countries
grouped as “Other” in the figure, including India, Mexico, and Brazil, were expected to
experience oil consumption growth rates 10 to 30 percent higher than the world average. In
2015, China’s consumption rose 6.3%, India’s decreased 3.2%, Brazil decreased 4.2%, Mexico
decreased 1.1%, and the United States increased 1.6%. As a whole, Europe Union rose 1.5%,
Africa 3.2%, and Asia Pacific (includes China) rose 4.1%. ( B.P. Statistical Review, 2016).
Petroleum 1, slide 4 here
In 2013, global oil production increased by 557,000 barrels per day (bpd), reaching a new
all-time high of 86.8 million bpd. Despite increasing consumption, production increased only
0.6 percent over 2012. After declining in 2009, global crude oil production increased 4 years in a
row. U.S. production increase was 1.1 million bpd, while global oil global production declined
by 554,000 bpd. (Rapier, 2014). The U.S. gain in oil production was the largest year over year
gain for any country in 2013, and the largest gain in US history. The United Arab Emirates had
second-largest increase with a gain of 248,000 bpd over 2012, and Canada increased 208,000 bpd
over 2012, the only three countries in the world to record an increase of more than 200,000 bpd.
As the graph shows, U.S. conventional oil production was on a steady decrease from 1984-2007,
when fracking output kicked in. US Oil production has been at near record levels reaching
293,617 barrels in May, 2015 (record is 310,320 barrels in November, 1970) in the past couple of
years. (U.S. Energy Information Administration, 2016).
Petroleum 1, slide 5 here
At any point while using petroleum, from drilling to final consumption, problems can
develop. Petroleum may be released into the environment. Petroleum-derived hydrocarbons and
chlorinated solvents are the most common contaminants of ground water (Averett and McKnight,
1988). Most often the release is accidental, through carelessness, poor design, or shear bad luck.
Accidents may happen during shipping, such as the Torrey Canyon and Exxon Valdez spills, or
through leakage at offshore facilities such as the Santa Barbara channel incident. Pipeline
ruptures on land have produced large terrestrial spills. Sometimes the release is deliberate, as in
the destruction of the oil fields in Kuwait or in cleaning and flushing of fuel tanks by ships and
the discharge of the flush into the ocean. Occasionally, oil spills are the result of natural
leakage. Whatever their origin, petroleum spills represent local to regional environmental
problems, often of considerable severity. The cost of cleaning up petroleum contamination is
usually very high, and the results of the cleanup are problematic.
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Environmental Geochemistry, GLY 4241/5243, © David Warburton, 2015
Petroleum 1, slide 6 here
Petroleum is a complex mixture. It contains a great variety of organic compounds.
Petroleum from different sources has different compositions and different properties.
Petroleum 1, slide 7 here
The environmental problems generated by petroleum spills will depend a great deal on the
original composition of the petroleum. Cleanup efforts need to done in accord with the nature of
the material spilled. Refined petroleum products, such as gasoline, diesel fuel, jet fuel, home
heating oil, etc. present problems that are much different from that of petroleum. Cleanup
procedures need to be developed and applied for each derivative.
Considering the tremendous environmental risks associated with the use of petroleum,
phasing out all use of the substance quickly might seem prudent. Unfortunately the use of oil is a
critical part of the energy infrastructure of all developed nations, and is often a crucial part of the
infrastructure of less developed countries. If the spigot were turned off, incredible social and
economic devastation would quickly follow. The problems associated with the naturally
enforced phase out of petroleum as supplies are exhausted will be traumatic enough.
Petroleum 1, slide 8 here
THE CHEMISTRY OF PETROLEUM
Petroleum is composed of many organic compounds, more than 75% of which are
hydrocarbons. Hydrocarbons are composed of hydrogen and carbon. Organic compounds are, in
principle, created by living organisms. In petroleum, some organic compounds may result from
metamorphosis of organic matter. The fantastic number and variety of organic compounds are
the result of the chemistry of carbon itself.
Petroleum 1, slide 9 here
Carbon atoms are small and possess four valence electrons. This means that carbon can
form bonds with up to four other atoms. Generally these bonds are covalent, involving the
sharing of electrons between atoms. The possibility of double bonds, involving the sharing of
two electrons, and triple bonds, involving the sharing of three electrons, also exist. Carbon
compounds may also form ring structures, where the head and tail of a carbon chain are bonded
together. Other compounds may also be associated with petroleum.
Petroleum 1, slide 10 here
These compounds, which usually contain hydrogen and carbon, also contain other elements such
as sulfur, nitrogen, or oxygen. Other atoms may range from trace amounts up to 4% sulfur, 1%
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Environmental Geochemistry, GLY 4241/5243, © David Warburton, 2015
nitrogen, and lesser amounts of oxygen (Hunt and O'Neal, 1966). Small amounts of metals may
also be presence. Metal amounts are generally in the parts per million range. The range for
crude oil from California, Kansas, Texas, Kuwait and Morocco for various metals was iron, none
to 31 ppm, nickel, 0.8 to 46 ppm, vanadium, 0.6 to 49 ppm, and copper, 0.1 to 1.1 ppm (Horne,
1978).
Petroleum is usually described as groups of compounds. Each group has similar
properties. This approach has great practical value in that it allows us to consider a very complex
mixture as a few groups. The names given to these groups also simplify the discussion.
Nevertheless, it must be realized that differences between compounds within the group do exist,
and that these differences may be quite significant from an environmental perspective.
Petroleum 1, slide 11 here
Hydrocarbon properties vary regularly with increasing molecular weight. As molecular
weight increases, the melting point, boiling point, and density of the compound increase. This is
true also of many other related organic compounds.
Petroleum 1, slide 12 here
Petroleum is often conceptually divided into ?fractions” based on the number of carbon atoms in
the compounds or on boiling point. As the result of the relationship between molecular weight
and boiling point, the two schemes are nearly identical.
Petroleum 1, slide 13 here
Natural gas, often associated with petroleum, contains one to four carbon atoms (C1 to C4). The
compounds from C6 to C10 makes up the gasoline fraction. Kerosene is composed of C10 to C16
compounds. C17 to C22 compounds make up lubricating oils and petroleum jelly. Those C22 and
C29 are often called tar or asphalt (Krauskopf, 1979).
Petroleum 1, slide 14 here
The video demonstrates some of the properties of petroleum and shows how it can be
distilled.
Petroleum 1, slide 15 here
Table 15 - 2 summarizes the properties of a few selected normal alkane hydrocarbons of different
carbon number.
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Environmental Geochemistry, GLY 4241/5243, © David Warburton, 2015
Table 15 - 2 Physical properties of selected normal alkanes
FORMULA
NAME
FREEZING
POINT, C
BOILING
POINT, C
DENSITY,
G/CM3
CH4
Methane
-182
-161
Gas
C2H6
Ethane
-183
-89
Gas
C3H8
Propane
-190
-45
Gas
C4H10
Butane
-138
-1
Gas
C5H12
Pentane
-130
36
0.626
C6H14
Hexane
-95
68
0.659
C7H16
Heptane
-90
98
0.684
C8H18
Octane
-57
125
0.703
C9H20
Nonane
-51
151
0.718
C10H22
Decane
-30
174
0.747
C11H24
Undecane
-27
195
0.740
C16H34
Hexadecane
18
287
0.773
After Krauskopf, 1979, p.232
Petroleum 1, slide 16 here
Hydrocarbons may also be classified by structural properties. One classification scheme
breaks petroleum hydrocarbons into paraffins, cycloparaffins, aromatics, naphtheno-aromatics
and residual fractions.
Petroleum 1, slide 17 here
Paraffins, also called alkanes, are split into normal paraffins and isoparaffins. A normal paraffin
is a linear chain of carbon atoms. Each carbon atom in the interior of the chain is bonded to
exactly two other carbon atoms. Paraffins make up about 25% of crude petroleum. They are
usually in the low boiling (40 - 230C) fractions.
Petroleum 1, slide 18 here
An isoparaffin consists of a straight chain of carbon atoms with at least one branch. At the
branch, one carbon atom is bonded to three other carbon atoms. Multiple branches off the
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Environmental Geochemistry, GLY 4241/5243, © David Warburton, 2015
straight chain, or branches off branches, are possible. The dominant isoparaffins are the ones
with the fewest and simplest branches.
Petroleum 1, slide 19 here
Cycloparaffins are also known as cycloalkanes or naphthenes. They are ring structures
such as cyclohexane or 3,3,o-bicyclo-octane. Alkyl side-chains attached to the ring are common.
An example is 1,2-dimethylcyclopentane. Cycloparaffins make up 30-60% of crude petroleum.
The most common cycloparaffins have a single ring, generally with five or six carbon atoms
(cyclopentane or cyclohexane). Compounds with up to six rings are common, and structures
with up to ten rings may be found in high-boiling fractions (Stoker and Seager, 1977).
Petroleum 1, slide 20 here
Aromatic hydrocarbons are also cyclic. The aromatic hydrocarbons have delocalized
electrons shared around the rings. These delocalized electrons make the bonds stronger than
single bonds, but less than true double bonds. Benzene is the simplest aromatic hydrocarbon.
Petroleum 1, slide 21 here
Benzene and its derivatives are the most common aromatic hydrocarbons in the low-boiling
fractions. Poly-cyclic aromatics are less common, and are found in higher-boiling fractions.
Aromatic hydrocarbons are less common than paraffins or cycloparaffins in most crude
petroleum.
Petroleum 1, slide 22 here
Naphtheno-aromatics, also called cycloalkanoaromatics, are combinations of the first
three types. They are found in the higher boiling fractions (generally around 300C).
Petroleum 1, slide 23 here
The structure is usually a fusion of an aromatic and a cycloparaffin ring, often with paraffins
present as alkyl branches.
Petroleum 1, slide 24 here
The residual fraction is composed of all types of high-boiling hydrocarbons, and the
composition of most of these compounds is not known. It is known that these compounds often
contain sulfur, nitrogen, oxygen, and trace metals. The compounds are often heterocyclic, with
rings of both the cycloparaffin and aromatic type. Heterocyclic rings may be connected by short
normal paraffin chains. A summary of the composition of crude petroleum by the classes is
shown in Table 15 - 3.
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Environmental Geochemistry, GLY 4241/5243, © David Warburton, 2015
Petroleum 1, slide 25 here
Table 15 - 3 Petroleum Composition by Fraction
Fraction Description
Number of
Carbon Atoms
Crude Petroleum
(% by weight)
Boiling point
range (C)
Paraffins
C6 - C12
0.1 - 20
69 - 230
C13 - C25
0+ - 10
230 - 450
C6 - C12
5 - 30
70 - 230
C13 - C23
5 - 30
230 - 405
C6 - C11,
Mono- and
dicyclic
0-5
80 -240
C12 - C18,
Polycyclic
0+ - 5
240 - 400
C9 - C25
5 - 30
180 - 400
10 - 70
> 400
Cycloparaffins
Aromatic
Naphthenoaromatic
Residual,
including heterocycles
After Moore et al., 1973
SOLUBILITY OF PETROLEUM HYDROCARBONS IN WATER
Various components of petroleum are soluble in water to different degrees. More data are
available on the solubility of hydrocarbons in distilled water than in sea-water. For those
substances where data is available in both distilled and sea-water, the solubility of the
hydrocarbons in sea-water is less than in distilled water.
Petroleum 1, slide 26 here
Table 15 - 4 lists the solubility of selected normal alkanes. Generally, the longer the hydrocarbon
chain, the less soluble the hydrocarbon, although many irregularities exist.
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Environmental Geochemistry, GLY 4241/5243, © David Warburton, 2015
Table 15 - 4 Solubilities of n-alkanes in Water
Compound
Number of Carbon
Atoms
Solubility in Distilled
Water (ppm)
Methane
1
24
Ethane
2
60
Propane
3
62
n-Butane
4
61
n-Pentane
5
39
n-Hexane
6
9.5
n-Heptane
7
2.9
n-Octane
8
0.66
n-Nonane
9
0.220
n-Decane
10
0.052
n-Undecane
11
0.0041
n-Dodecane
12
0.0037
0.0029
n-Tetradecane
14
0.0022
0.0017
n-Hexadecane
16
0.0009
0.0004
n-Octadecane
18
0.0021
0.0008
n-Eicosane
20
0.0019
0.0008
n-Hexacosane
26
0.0017
0.0001
n-Triacontane
30
0.002
n-Heptacontane
37
10-8 *
* Extrapolated; Data after Clark and MacLeod, 1977
Petroleum 1, slide 27 here
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Solubility in SeaWater (ppm)
Environmental Geochemistry, GLY 4241/5243, © David Warburton, 2015
Table 15 - 5 presents solubility data for branched or isoalkanes. The isoalkanes are all more
soluble than n-hexane, which has the same number of carbon atoms. 2,2-dimethylbutane, a
compound with two branches, is about twice as soluble as n-hexane. Generally, branching
increases solubility. The designation 2, 3, etc. shows the number of the carbon atom that the
branch is attached to, starting from the end of the chain nearest the first branch.
Table 15 - 5 Solubility of Isoalkanes in Distilled Water
Compound
Number of Carbon
Atoms
Solubility in Distilled
Water (ppm)
2-Methylpentane
6
13.8
3-Methylpentane
6
12.8
2,2-Dimethylbutane
6
18.4
Data after Clark and MacLeod, 1977
Petroleum 1, slide 28 here
The cycloparaffins are much more soluble than the alkanes. Table 15 - 6 presents
solubility data for cycloparaffins. Like the alkanes, the cycloparaffins show decreasing solubility
with increasing carbon number. However, the rate of solubility decrease is less for the
cycloparaffins than for the alkanes. For example, cyclopentane is about four times more soluble
than pentane, but cyclooctane is twelve times as soluble as n-octane. Aromatics, cyclic
compounds with delocalized electrons shared around the ring, are the most soluble components
of crude petroleum by far.
Table 15 - 6 Solubility of Cycloparaffins in Distilled Water
Compound
Number of Carbon Atoms
Solubility in Distilled Water
(ppm)
Cyclopentane
5
156
Cyclohexane
6
55
Cycloheptane
7
30
Cyclooctane
8
7.9
Data after Clark and MacLeod, 1977
Petroleum 1, slide 29 here
Table 15 - 7 lists the solubilities of several aromatic compounds. Benzene, the simplest aromatic
compound, is nearly 200 times more soluble than n-hexane. As with the other hydrocarbons,
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Environmental Geochemistry, GLY 4241/5243, © David Warburton, 2015
solubility decreases as the carbon number increases, but this is complicated by branching, double ring
structure, etc. For example toluene has less than a third of the solubility of benzene. Toluene has one
methyl group substituted for a hydrogen atom attached to the ring. O-Xylene, which has two methyl groups
attached next to each other on the benzene ring, has about one-third the solubility of toluene. Ethylbenzene,
which has an ethyl group substituted for a hydrogen atom on the benzene ring, is slightly less soluble than
o-xylene, although it has the same number of carbon atoms. It is much less soluble than toluene, with a
methyl group instead of an ethyl group. Iso-Propylbenzene, with a propyl group attached to a benzene ring,
is even less soluble. Thus, the longer the side chain attached to the aromatic compound, the less soluble it
will be. Napthalene consists of two six-membered rings that have two carbon atoms common to both rings.
Table 15 - 7 Solubility of Aromatics in Water
Compound
Number of Carbon
Atoms
Solubility in
Distilled Water
(ppm)
Benzene
6
1780
Toluene
7
515
o-Xylene
8
175
Ethylbenzene
8
152
1,2,4-Trimethylbenzene
9
57
iso-Propylbenzene
9
50
Naphthalene
10
31.3
1-Methylnapthlene
11
25.8
2-Methylnapthlene
11
24.6
2-Ethylnapthlene
12
8.00
1,5-Dimethylnapthalene
12
2.74
2,3-Dimethylnapthalene
12
1.99
2,6-Dimethylnapthalene
12
1.30
Biphenyl
12
7.45
Acenapthalene
13
3.47
Phenanthrene
14
1.07
Anthracene
14
0.075
Chrysene
18
0.002
Data after Clark and MacLeod, 1977
10
Solubility in Seawater (ppm)
22.0
4.76
.71
Environmental Geochemistry, GLY 4241/5243, © David Warburton, 2015
Petroleum 1, slide 30 here
In the naphthalene derivatives, the solubility again decreases with the presence and
length of side chains. Biphenyl consists of two benzene rings linked by a single carbon-carbon
bond. Of the five compounds with twelve carbon atoms, ethylnaphthalene (an ethyl group
substituted for one hydrogen atom) is the most soluble. Biphenyl is next. Then the various
dimethylnaphthalenes follow with decreasing solubility. The solubility in sea-water, where data
is available, again indicate that most compounds are only about 60 - 70% as soluble in sea-water
as in distilled water.
Petroleum 1, slide 31 here
To understand the solubility of petroleum hydrocarbons in water in a general way, we
need to consider the nature of the substances involved. Water is composed of hydrogen and
oxygen. The electronegativity of hydrogen is 2.1 and that of oxygen is 3.5, for a difference of
1.4. Pauling (1960) says that an electronegativity difference of 1.4 corresponds to bond with
about 40% ionic character.
Petroleum 1, slide 32 here
Carbon has an electronegativity of 2.5. In hydrocarbons the electronegativity difference of 0.4
corresponds to about 5% ionic bond character. Water also has extensive hydrogen bonding. This
accentuates the ionic bond character. Therefore, the bonds in water are strongly polar; the bonds
in hydrocarbons are not.
Petroleum 1, slide 33 here
Shaw (1977) developed a hypothesis for the behavior of hydrocarbons in water. A
hydrocarbon molecule in water may be regarded as a cavity in the structure of the water. Water
molecules at the edge of the cavity are pulled away from the cavity by the strong hydrogen
bonding between water molecules. This orders the water molecules near the cavity edge. The
increase in order decreases entropy. The decrease in entropy means that energy must be supplied
to the system to get hydrocarbons in solution. Thus, hydrocarbons are generally of low solubility
in water. Indeed, hydrocarbons are thought of as hydrophobic.
Petroleum 1, slide 34 here
Hydrophobicity increases with increasing molecular weight and with increasing molar volume.
Small, compact hydrocarbons are usually the most soluble. These same molecules are also
volatile and are rapidly lost in most cases of petroleum spills. Heavier molecules with high
molar volume are retained and are the most problematic in petroleum spills.
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Environmental Geochemistry, GLY 4241/5243, © David Warburton, 2015
Petroleum 1, slide 35 here
Although we are discussing primarily hydrocarbons, it should be noted that the solubility
of hydrocarbons is greatly increased by the substitution of one or more polar functional groups
for a hydrogen atom. For example, alcohols are compounds with a hydroxy group (-OH)
substituted for hydrogen. The breakdown products (chemical, photochemical, and microbial) of
petroleum hydrocarbons are often smaller or have polar functional groups attached. This means
that the breakdown products are often of higher solubility than the original petroleum.
Petroleum 1, slide 36 here
The breakdown products with polar functional groups may act as natural dispersants. The polar
functional group is hydrophilic. Compounds that contain both hydrophobia and hydrophilic
regions may be called amphipathic (Robotham and Gill, 1989).
Petroleum 1, slide 37 here
Amphipathic molecules can bind to both water and hydrocarbons, thus making the hydrocarbons
more soluble in water. Common chemical and biological breakdown products of petroleum
hydrocarbons include the amphipathic substances acids, ketones, and quinones. Common
biological breakdown products include long-chain alcohols and acids. All may act as
dispersants.
Petroleum 1, slide 38 here
In addition anthropogenic dispersants exist. These include domestic and industrial detergents,
and substances deliberately applied to petroleum spills to act as dispersants. Unfortunately,
although dispersants may help to make a petroleum spill less visible, they often harm the
environment more than the original spill.
ENVIRONMENTAL SIGNIFICANCE OF DISSOLVED
HYDROCARBONS
Petroleum 1, slide 39 here
Why should we be more concerned about dissolved hydrocarbons than emulsified,
adsorbed, or complexed petroleum in water? Two papers claim that only in the dissolved form is
petroleum acutely toxic (Landrum et al., 1985; McCarthy et al., 1985). When petroleum is
absorbed or otherwise bound, the attraction is too strong to allow significant uptake by biological
organisms (Robotham and Gill, 1989). Thus, the most soluble compounds are the most
dangerous.
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Environmental Geochemistry, GLY 4241/5243, © David Warburton, 2015
Petroleum 1, slide 40 here
Traditionally the BTEX compounds are regarded as the most dangerous hydrocarbons. BTEX
stands for benzene, toluene, ethylbenzene, and xylene. One reason these compounds are so
dangerous is that they are significant components of refined petroleum products such as gasoline
and jet fuel. Spills of gasoline or jet fuel in the marine or terrestrial environments may have
severe consequences.
Petroleum 1, slide 41 here
Two short video interviews with Terri Tamminen, Author and Environmental Policy
Advisor, about BTEX compounds in gasoline.
Petroleum 1, slide 42 here
A short video clip about sources and risks from benzene in the home.
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4241LN15_pp_F16.pdf
November 3, 2016
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